An accurate road-model of an upcoming road segment is desirable for automated-vehicles and automotive active safety systems. Road-models that use a single plane to represent a travel-surface (e.g. a roadway) have been suggested. However, using a single plane is not always adequate as the travel-surface is not always planar, so the effects of road angle (crown, changing slopes) on the behavior of a vehicle moving on the travel-surface are not predictable.